Effects of delta9-tetrahydrocannabinol on social behaviour in mice: comparison between two vehicles.

Two vehicles for the intraperitoneal administration of delta9-tetrahydrocannabinol (delta9-THC) were compared, using aspects of social behaviour in mice and 5 doses of delta9- THC, with vehicle alone and saline control groups. 10% propane-1,2-diol-1% Tween 80-saline (vehicle B) seemed to be more effective than 1% Tween 80-saline (vehicle A) since depressant effects of --1 delta9-THC on behaviour tended to occur at lower doses with this vehicle. Few differences in behaviour could be detected among the three control groups. In general the overall number of behavioural acts decreased with increasing doses of delta9-THC, but with vehicle B low doses selectively decreased the number of 'social' (including aggressive) as distinct from 'individual' acts. Low doses of the drug in vehicle A sometimes stimulated behaviour, whereas with vehicle B such doses mostly produced depression; however, 2.5 mg/kg delta9-THC, in either vehicle, markedly increased the percentage of animals which showed both aggression and flight acts--a rare combination among controls. Our findings are consistent with other evidence that propylene glycol is an effective vehicle for the i.p. administration of delta9-THC.